The invention relates to a fabric for the sheet forming section of a papermaking machine comprising a double-layer or multi-layer fabric of interwoven longitudinal and transverse threads and additional transverse threads floating on the paper side.
Papermachine fabrics with additional transverse threads floating on the paper side have been known from U.S. Pat. Nos. 4,182,381 and 4,281,688 and from European Patent Publication No. 85 363. According to U.S. Pat. No. 4,182,381, the additional transverse threads are to reduce wear especially in the region of a loop seam. According U.S. Pat. No. 4,281,688, the transverse threads are so interwoven that equally long floats are formed on the paper side and on the running side, which is to prevent curling of the edges.
According to European Patent Publication 85 363, the additional transverse threads floating on the paper side are to facilitate the removal of the sheet, reduce the risk of marking, and increase the permeability. The additional transverse threads are so interwoven that they have minimum crimp. However, as a consequence, they project on the paper side so far that they interfere with the sheet formation. During cleansing of the fabric by high pressure water jets, projecting threads are frequently destroyed.
German Ausleggesschieft No. 32 24 236 and European Patent Publications Nos. 69 101, 93 096, and 117 856 disclose sheet forming fabrics in which longitudinal threads or transverse threads are interwoven in pairs, and the threads of each pair are mutually offset, but otherwise interwoven in the same way, so that on the paper side a regular weave pattern is formed. In case the pair-wise interwoven threads are provided in addition to ordinary interwoven threads, they supplement each other on the paper side in forming the same weave as the ordinary threads. The pair-wise interwoven threads have the purpose of joining two fabric layers, or two layers of transverse threads, to one another.